1. Field of the Invention
This invention relates to an intumescent fire-retardant coating composition containing a substantially water insoluble amide polyphosphate condensate. More particularly, this invention relates to an intumescent coating composition exhibiting excellent fire-retardant properties when applied to inflammable building materials, interior decorative materials such as plywood or fibrous panels, insulated electric wires and so on.
2. Description of the Prior Art
It is well known that ammonium polyphosphate can be used as an excellent fire-retardant additive for an intumescent coating composition. For example, British Patent No. 1,171,491 discloses that intumescent coating compositions containing a suitable amount of ammonium polyphosphate achieved a Class A fire rating in the ASTM E-84-50T fire retardant test when applied to a panel of yellow poplar heartwood with a coverage of about 150 ft.sup.2 /gal.
Ammonium polyphosphates used as a fire-retardant additive in conventional intumescent coating compositions are represented by the general formula: EQU H.sub.(n.sub.-m).sub.+2 (NH.sub.4).sub.m P.sub.n O.sub.3n.sub.+ 1
wherein n is an integer having an average value greater than 10 and m/n has an average value between 0.7 and 1.1, and are defined as having a water solubility of about 5 grams or less per 100 cc of water, evaluated by slurrying 10 grams of the solids in 100 cc of water for 60 minutes at 25.degree.C.
Although the ammonium polyphosphate represented by the above formula is said to be "substantially water-insoluble", it is soluble in water to some extent since, in actuality, the solubility of 10 g of ammonium polyphosphate is about 1 to 5 g per 100 cc of water measured in the above-described manner. Hence, a coating composition containing this ammonium polyphosphate does not have sufficient water-resistance, moisture-resistance and weather-resistance, although it is superior to a coating composition containing conventional water-soluble ammonium phosphates such as ammonium dihydrogenphosphate.
Furthermore, there are very important requirements for an intumescent fire-retardant coating composition which is to be applied to insulated electric wires. Generally polyethylene, polyvinyl chloride, natural rubber, synthetic rubber and the like are used as an insulator for insulated electric wires. These are all inflammable materials and have low resistance to fire and high temperature. Thus, when the wires are exposed to a fire or high temperature, inferior insulation or a short circuit in the electric line can happen to result in very serious hazards. Further, polyvinyl chloride which has a relatively higher fire-retardant property has another problem in that a toxic halogen-containing gas is generated when it burns, even though it is fire-retardant initially.
Heretofore, generally a dispersion composition of antimony trioxide, inorganic fiber and so on in an organic synthetic resin emulsion or a mixture of a water-soluble phosphate derived from orthophosphoric acid and an organic synthetic resin or a reaction product thereof have been used as fire-retardant coating compositions for insulated wires, and these compositions have been applied to the surface of insulated wires by spraying or painting. However, fire-retardant coating compositions as described above have various defects with regard to the properties desired. The former composition does not form an intumescent layer having heat-insulating properties at the time of fire, since it does not contain an intumescent material. Accordingly, a large amount of the composition must be coated on the insulated wires in order to obtain a desired fire-retardant effect. On the other hand, the latter composition has inferior weather resistance since it contains a water-soluble material, although it is intumescent. That is, the coatings formed on insulated wires deteriorate remarkably and the fire-retardancy of the coatings decreases to a great extent when exposed under high moisture conditions or contacted with water.
As described above, both the conventional intumescent fire-retardant paint for the treatment of inflammable materials and the conventional intumescent fire-retardant coating composition for the treatment of insulated wires have considerable restrictions in practical use, since they do not have sufficient weather-resistance, particularly water-resistance and moisture-resistance.
As a result of an extensive investigation in order to eliminate such disadvantages, it has now been found that, when an intumescent fire-retardant coating composition containing a substantially water-insoluble amide polyphosphate condensate is coated on the surfaces of inflammable materials or insulated wires, the properties of the coating such as water-resistance, moisture resistance and weather-resistance can be greatly improved because of the extremely low solubility of the composition in water and, at the same time, the coating has superior fire-retardant properties because an effective heat-insulating layer is formed on substrates due to its intumescent properties.